Mulch has long been used in agriculture to enhance the growth of plants and to minimize the growth of weeds. Since the earliest times, mulch has taken the form of weeds, grass clippings, chips, and all kinds of biodegradable plant matter. The object is to cover the soil around the stem of the growing plant and over the roots to screen sunlight from the adjacent soil and minimize the growth of weeds. If there is no sunlight, the weeds will not grow. The mulch will typically also allow water from irrigation or rain to percolate through the soil beneath the mulch. The overlying mulch layer will inherently slow the evaporation of water from the soil, and in theory will hold more water near the roots of the plant to increase its growth. The need for such mulch is most pronounced while the plant is young and/or after planting or transplanting, at which time it is most vulnerable to the effects of weeds, which take moisture and nutrients from the soil. Some young plants may also need a degree of protective shade during this vulnerable period, particularly in hot climates.
In this century, various modifications of the age old use of biodegradable vegetable matter as a mulch have been tried with varying success. In general, these variations have taken the form of a variety of mats, collars, and shoes which fit about a plant stem. Some of these devices, in addition to inhibiting the growth of weeds in the vicinity of the plant, have demonstrated other useful functions; for example, some mulches may help keep the soil around the plant moist, by reducing evaporation and encouraging condensation on the underside of the device. Furthermore, in cold weather such mulches may help to keep the roots of the plant at acceptable temperatures by shielding the soil surface from the wind and providing a measure of insulation against ground frost.
Various kinds of artificial mulch are known or have been proposed, the simplest being sheets or strips of opaque plastic film, usually black or green. This is commonly used by strawberry growers around their plants. Such film, however, is very prone to being lifted by the wind, and, since it is subject to being folded and wrinkled, may adversely affect the distribution of moisture to the plant during the watering. Furthermore, it is often desired to grow such plants in gardening pots; artificial mulches consisting of simple sheets of plastic film typically have no convenient means by which they may be anchored in a gardening pot, and thus are easily lifted by the wind or other forces and disarranged.
Another simple type of artificial mulch takes the form of a cardboard sheet having a central opening for receiving the stem of a plant. A slit extending from the opening to an edge of the sheet enables the sheet to be deformed to provide a passage by which the stem may be inserted into the opening. Disadvantages of this type of artificial mulch are its tendency to distort and curl up at the edges, so reducing both its efficiency and its ability to permit a ready supply of moisture to the plant. Furthermore, the slit may cause a gap in the coverage provided by the sheet, thus uncovering a portion of the soil surface which can then be invaded by weeds.
Another kind of artificial mulch that has been proposed consists of a pair of chevron-shaped flexible mats which are placed in opposed relationship on the ground on either side of the stem of the plant so that the stem protrudes through a diamond-shaped opening formed at the apices of the two reentrant sides of the mats. Apart from the placing turf thereon, which represents a slow and labor-intensive process, no means are provided for maintaining the mats in position, and an excessive overlap of the mats is required to complete the installation, wasting a significant amount of mat material.
Yet another type of artificial mulch, described in U.S. Pat. No. 4,794,726 to Fawcett et al. (1989), consists of a mat formed of a woven plastic material having aluminum flakes bonded thereto for reflecting sunlight toward the underside of the leaves on the plant. A slit is provided in the mat, from one edge to the center hole, in order to place the mat around a growing plant. No means are provided for insuring that the gap created by the slit is kept closed. This mat also appears to be relatively expensive, which is a significant disadvantage for use in reforestation projects and the like, where a vast number of individual mulch rings may be used once and left permanently installed about the seedlings or saplings.
A number of other artificial mulches have similar arrangements of central stem openings and radial installation slits which lack means for ensuring that the gaps formed by the slits are kept closed. Such mulches include the following: British Pat. No. 2,053,640 to Mellor (1981) discloses a mulch shoe consisting of a thin, opaque web of stiff material having a central hole and transverse slit for installation. The web has channels for collecting and distributing water. The relatively stiff material of this device also may damage the stem of the plant if it is left installed over an extended period of growth. U.S. Pat. No. 3,857,195 to Johnson (1974) discloses a mulch packet having a water permeable compartment for holding fertilizer and a perforated plastic base through which water is discharged into the soil after percolating through the fertilizer; the central portion of the packet may be punched out to provide an opening for the trunk of a plant, and a radial slit extends from the opening to the periphery of the packet. British Pat. No. 1,378,663 to Basnayake (1974) discloses a mulch ring, having a central aperture and radial slit, which is made of an impervious top sheet underlain by second and third sheets which contain nutrients, fungicides, insecticides, and/or herbicides.
Another mulch ring, described in British Pat. No. 1,381,679 to Williams (1975), consists of a cover having small ventilation holes and a central hole and a slot for installation. The cover is thicker near its outer edge, so as to support the wheels of lawn mowers which may run over it. An overlapping portion closes the installation slot, however, a separate clip is required to secure the overlapped portions together; accordingly, this device requires extra parts and labor which reduce both the economy and speed of installation. British Pat. No. 1,284,768, also to Williams (1972), discloses a substantially similar device which exhibits similar disadvantages.
A number of other artificial mulches similarly require undesirable extra parts, labor, and time to install. Such mulches include the following: U.S. Pat. No. 3,727,347 to Barnes (1973) discloses an artificial grass-like mat which has a central opening which fits around a tree and a radial slit; a staple must be inserted through the mat to fasten it to the ground and to hold the slit closed. U.S. Pat. No. 3,059,378 to Noras (1962) discloses a pad made of semi-dry concrete mix in two or more complementary parts with a central aperture for the accommodation of a tree; staples must be inserted to hold the parts together. It would also be necessary to remove this device following a period of growth in order to accommodate the increased diameter of the trunk.
U.S. Pat. No. 3,005,287 to Dudley (1961) discloses another artificial mulch which requires extra parts and labor to install. This device includes a plastic disc having a central opening and a radial slit; plant food cups are mounted in an annular trough which is provided with drain holes. A depending peripheral flange of the disc is buried in the soil to install the disc, and perforated, flanged tubes are then driven through some of the holes of the trough.
U.S. Pat. No. 2,949,698 to Downey et al. (1960) discloses a mulch device consisting of a relatively thick square pad of resilient fibrous material which has a central opening and a radially extending oblique cut or slot which intersects the pad surfaces at an angle of approximately 45.degree.. The thick pad is flexed apart and fitted around the trunk of a plant, the resilience of the pad causing the sides to spring together until the oblique slot is closed; the cohesion of the fibrous material of the pad enhances the seal thus formed. This arrangement relies on having the pad made out of a relatively thick, and hence expensive, sheet of material.
U.S. Pat. No. 2,209,891 to Hoover (1940) discloses a cage-like structure which is fitted about a plant to support organic mulch (e.g. leaves) above the surface of the ground to promote drainage and air circulation. In one version, the device consists of a relatively complex wire cage constructed in two semi-circular sections having spike portions which can be driven into the earth to secure the halves in position. This device is not itself a mulch ring; rather, it supports organic mulch which is packed on top of it. Furthermore, installation of the device would appear to require extensive manual fitting.
Each of the above described products may have some beneficial effect under certain circumstances. As noted, however, each of the products also has certain deficiencies in terms of expense and efficiency of installation. These disadvantages are magnified in applications, such as reforestation, which call for the use of a very large number of mulch devices, which are preferably left permanently installed about the trees. Furthermore, none of the above described products appears to be able to be securely mounted in the mouth of a planting pot, or to provide shade which may be needed by a young plant. Accordingly, what is needed is an inexpensive artificial mulch device which can be quickly installed with a minimum of labor and parts, and which can be left permanently installed about the plant as it grows. Furthermore, there is needed such a mulch device which can be mounted in the mouth of a planting pot so as to remain secured therein against the wind and other forces, as well as for a mulch device which can provide protective shade where desirable.